dome construction

[mario]

Can anyone discuss the advantages/disadvantages of cutting all dome bricks into trapezoidal half bricks and laying the bricks on 2 1/2" x 4 1/2" edge while keeping a uniform mortar joint on each brick (in the parabolic direction) in order to accomplish the shape of the dome versus laying half bricks on side with shim and no mortar at oven face and thick joint at outside dome face?

I'm curious which method might perform better with heating/cooling cycles and last longer over time. And I'm also curious if having only brick face in oven without mortar is some type of advantage or if this method is mosty preferred due to ease of construction without the use of complicated forms.

Thanks, Mario

[Marcel]

Save brick, save work, save diamond blade

Can anyone discuss the advantages/disadvantages of cutting all dome bricks into trapezoidal half bricks and laying the bricks on 2 1/2" x 4 1/2" edge while keeping a uniform mortar joint on each brick (in the parabolic direction) in order to accomplish the shape of the dome versus laying half bricks on side with shim and no mortar at oven face and thick joint at outside dome face?

(Marcel) Hi, Mario,

(M) If I understand your proposal then I would say cutting bricks to the shape of 3 dimensional trapezoids,with 4 rather than 6 parallel sides, means you lose brick, work time, and diamond dust on your blade. The forum reading I've done suggests that the dome can be constructed with almost any shape of brick and that if the total brick volume is the same, irrespective of shape, that the thermal properties would be essentially constant. Filling the voids between the bricks with wedges of mortar or "slabs" of mortar should not greatly impact the dome strength. You end up with the same shape "igloo".


(Mario) I'm curious which method might perform better with heating/cooling cycles and last longer over time. And I'm also curious if having only brick face in oven without mortar is some type of advantage or if this method is mosty preferred due to ease of construction without the use of complicated forms.

(Marcel) I'm not thermal engineer so take this comment as that of a novice, but it seems that having as little refractory mortar as possible exposed to the flame would lessen the chance of mortar cracking. In my opinion, it also looks nicer, though you'll seldom peer inside your oven.

Thanks, Mario

(Marcel) On a somewhat related matter but dealing more with the orientation of simple 1/2 bricks, consider exploring the following 2 threads from earlier Forum discussions:

http://www.fornobravo.com/forum/showthread.php?t=253

http://www.fornobravo.com/forum/showthread.php?t=256

Ciao,

Marcel

[mario]

dome construction

Thank you for your insights and your very clear photos, Marcel!

You understood my proposal well; And from your explanation, it seems that an evenly bedded mortar joint (some of which would be eposed to flame) may not increase durability of dome, despite the extra effort required.

Thanks again, Mario

[PizzaMan]

I believe I would...

I only cut the half bricks into trapazoids for the last 3 rows at the top. I belieave I would have begun doing that much earlier.

I cannot address the longevity or heating differences; I can only say that it would have been somewhat easier to lay up had I cut the bricks after, say...the first three rows.

Fitting in those trapazoids went so smoothly and quickly I was quite surprised. And I did not even need mortar for the top 10 pieces. They fit in so snuggly that I had the gently tap the last three or pieces in together at the same time. The whole structure immediately firmed up, and I was so excited that I did not wait to remove the styrofoam vane-type forms. It was immediately very strong...selling me on the inherent strength of the dome-style construction process.

No, it may not make a huge difference, but i still smile when I recall how nicely the last part of the dome went together with a minimum of mortor. That's no mortar to clean up, to spall, or to interfere with the beauty of the structure.

And I have to believe that that is all better in the long run.

Just my $.02...

[james]

Pizza man,

Do you have any dome photos? Sounds tight.

Here is a dome photo that Keith just sent.

James

[mario]

alternative dome construction

Thank you, Pizzaman, for sharing your trapezoidal experience with me. Glad to hear of your construction successes and that you would implement that method even more so for your next oven!

James, that's one for and one against the alternative trapezoid method. Do you have any insights or comments?

Is the benefit gained of having a "global keystone locking dome" by setting the trapezoidal half brick on edge so that the outside arc of the dome gets a 4.5" dimension for each half brick while the inside arc gets a smaller dimension (maybe about 4"?), worth the effort of extra cutting and additional form work? This method would most likely utilize a more uniform mortar bed along the bottom edge of each brick. I'm wondering how additional mortar on the inside face of dome might affect long term durability and thermal performance of oven. Another thought: one could figure the trapezoidal shape to account for a decreasing mortar bed thickness (from outside face of dome to inside face of dome) so that mortar joint on inside face was not excessively thick, and thus, less vulnerable to high heat damage. I'm thinking that the use of some form of this alternative could quite possibly be an advancement in structural strength, given the beneficial wedge-shaped construction, but may represent risks not worthy of its benefit. Any thoughts?

Thanks, Mario

[james]

Mario,

As you are building a larger oven and an oven that is going to be used commercially, I would considering doing the extra cuts to get the bricks tighter, and with less mortar exposed into the interior of the oven. Better durability for the longer firing periods you are going to have -- 12 hours a days, 365 days a year vs. a handful of firings a month.

I would also consider using a real refractory mortar, not fireclay mortar with Portland.

You can buy Refrax from Forno Bravo, or use calcium aluminate (not portland), to the following recipe:

1 part calcium aluminate
3 parts sand
1 part fire clay
1 part masons lime

It is a little harder to work wtih, but is more heat reistant, will last longer and will even give your oven better performance. It will get hot when it sets, which is pretty interesting when you are working with it.

James

[tshands]

Dome question

you guys have built some impressive ovens and obviously are quite talented. I'm trying to figure out if I have the skill to do this. The dome seems to be the most daunting part of the project to me at this point and one thing I think I have learned from all is to have a clear idea of each step in your mind before tearing the backyard up. My wife says I'm famous for starting a project gung ho only to fizzle out with the goal line in sight. I cound never live it down if I ended up with a massive nonfunctional masonry monument in my backyard ...just as well go ahead and bury me underneath it and scribe my name on it. I'm going to roughly detail how I understand the dome process and please comment where you can. Once the floor is laid and circle drawn the for the oven ( prob 42-43" dia), styrofoam vane in place ,the first course of !/2 bricks are laid on edge (4 1/2" h) with the 2nd and subsequent courses laid flat (2 1/2" h). These first 2 courses go straight up, while the next ones begin to curve inward to form the dome. How do you get this course to curve inward to lay against the vane? Do you use wood shims to do this or lay down a bed of mortar on the outside and tap into place ( as I understand it one wants little or no mortar on the inside portion of the dome) ? seems to me if shims were used to hold the correct angle, you could fill the gaps with mortar (special type?) , incl the void left by shim removal, and require less skill than the traditional " buttering" masoners use. At some point in the process, it may become advantageous to cut the bricks into trapezoids to fit better and leave less of a gap on the outside to fill. Finished interior height for a 42' oven should roughly be 18"? Concerning vane construction, or the shape, does anyone have a special process for laying this out other than by looking at it? Thanks for any input and Happy Easter to you and your families. Tom Shands.

[Marcel]

16 vanes or one blue beach ball?

(M) Tom, I used 8 vanes and should have gone for 16. But if I had it to do over again I think I'd re-examine the ball idea as explained in the post below:

http://www.fornobravo.com/forum/showthread.php?p=2592


(M) If the link above is not clickable, just Copy-Paste it into your browser window.

(M) Look for a picture of a blue ball toward the bottom. I'd write to Davy, the builder to ask if it continued to work out well for him. He lists his email as abpo@shaw.ca

Ciao,

Marcel

[tshands]

Thank you Marcel for the info. Tom